Organophosphorus-catalyzed relay oxidation of H-Bpin: electrophilic C–H borylation of heteroarenes

Abstract

© The Royal Society of Chemistry 2020. A nontrigonal phosphorus triamide (1, P{N[o-NMe-C6H4]2}) is shown to catalyze C-H borylation of electron-rich heteroarenes with pinacolborane (HBpin) in the presence of a mild chloroalkane reagent. C-H borylation proceeds for a range of electron-rich heterocycles including pyrroles, indoles, and thiophenes of varied substitution. Mechanistic studies implicate an initial P-N cooperative activation of HBpin by1to giveP-hydrido diazaphospholene2, which is diverted by Atherton-Todd oxidation with chloroalkane to generateP-chloro diazaphospholene3. DFT calculations suggest subsequent oxidation of pinacolborane by3generates chloropinacolborane (ClBpin) as a transient electrophilic borylating species, consistent with observed substituent effects and regiochemical outcomes. These results illustrate the targeted diversion of established reaction pathways in organophosphorus catalysis to enable a new mode of main group-catalyzed C-H borylation.